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Progress In Electromagnetics Research
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EXTRACTING COUPLING MATRIX AND UNLOADED Q FROM SCATTERING PARAMETERS OF LOSSY FILTERS

By R. Wang and J. Xu

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Abstract:
This paper presents a method for extracting the coupling matrix and the unloaded Q from the measured (or electromagnetic simulated) S-parameters of a narrow band cross-coupled resonator bandpass filter with losses. The Cauchy method is applied to determine the characteristic polynomials of the S-parameters of a filter in the normalized low-pass frequency domain. A five-parameter optimization method is proposed to obtain the unloaded Q and remove the phase shift of the measured S-parameters, which is caused by the phase loading and the transmission lines at the input/output ports of a filter. Once the characteristic polynomials of the S-parameters with the phase shift removed have been determined, the coupling matrix of a filter with a given topology can be extracted using well established techniques. Two application examples are given to illustrate the validity of the proposed method.

Citation:
R. Wang and J. Xu, "Extracting Coupling Matrix and Unloaded Q from Scattering Parameters of Lossy Filters," Progress In Electromagnetics Research, Vol. 115, 303-315, 2011.
doi:10.2528/PIER11021604
http://www.jpier.org/PIER/pier.php?paper=11021604

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